JP2010270287A - Ink set, method for inkjet recording, and inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set suitable for forming a color image on plain paper using color ink suitable for a subtractive color mixing method such as cyan, magenta, and yellow ink. <P>SOLUTION: The ink set includes a plurality of water-based ink containing color materials and is discharged from a recording head for inkjet, wherein the surface tension of the water-based ink is ≤34 mN/m. The ink set includes a combination of water-based ink of at least three hues, i.e. cyan, magenta, and yellow, wherein a combination of water-based ink of at least two out of the three hues includes two water-based ink which have the same hue but provide aggregation of color materials upon contact. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink set for ink jet recording, an ink jet recording method using the ink set, and an ink jet recording apparatus.

  With the widespread use of inkjet recording systems, improvements in the quality of printed matter and improvement in robustness are being promoted. Furthermore, recently, ink droplets having a size of 5 pl or less have become mainstream, and there is an increasing demand for printing various color information such as photographic images of digital cameras and homepages on plain paper on both sides. In order to improve the quality of a color image on plain paper, first, it is required that the character quality has a high density, sharpness, and no blur. It is also important to reduce the bleeding (bleed (phenomenon)) of the boundary portions of different colors caused by the contact of recording inks of a plurality of colors and the contamination caused by the line markers.

  The following various methods are disclosed with respect to these subjects. For example, Patent Document 1 uses two types of inks having different penetrability for a predetermined hue, and of these, an ink having a higher penetrability is mainly used at a boundary portion with an ink different from the predetermined hue. A method for reducing bleed by performing recording using this method is disclosed. Further, Patent Document 2 discloses a method for reducing bleeding by causing aggregation due to a chemical reaction in all combinations of inks when forming a color image using at least three colors of ink. . In Patent Document 3, two types of inks having different polarities are used as black ink, so that the black ink has a sufficient image density, has excellent water resistance and light resistance of a recorded image, and forms a color image. An ink set is disclosed that prevents bleeding even when it is performed.

JP-A-9-193529 JP 2001-172536 A JP 2000-7964 A

The present invention relates to a suitable ink set, an ink jet recording method, and the like when a color image is formed on plain paper using color inks suitable for the subtractive color mixing method, that is, cyan, magenta, and yellow inks. is there. The problems to be solved by the present invention are summarized below.
1) Ink is fixed at high speed.
2) Line marker resistance of the image is good.
3) Do not bleed between colors.
4) Double-sided printing is possible with no problems in the back-through and scratch resistance.
5) A clear image can be obtained with a high density in both single color and mixed color inks.

  With respect to these problems, according to the conventional method described above, the bleed between specific colors can be satisfied to some extent. However, recently, the number of ink shots that are larger than that of character-centered data is also increasing, so it is possible to achieve higher image quality with high-speed fixing on plain paper. There is a strong demand. Therefore, there is a demand for a recording method that can fully satisfy all of the above-mentioned problems at the same time. From the standpoint of energy saving, suitability for double-sided printing is also important.

  Accordingly, an object of the present invention is to provide an ink set that satisfies all of the above problems 1) to 5), an ink jet recording method using the ink set, and an ink jet recording apparatus.

  The above object is achieved by the present invention described below. That is, the first invention of the present invention is an ink set comprising a plurality of water-based inks containing a color material discharged from an inkjet recording head, wherein the surface tension of the plurality of water-based inks is 34 mN / m, and the ink set has a combination of water inks of at least three hues of cyan, magenta, and yellow, and the combination of water inks of at least two hues of the three hues has the same hue. The ink set is composed of two water-based inks that cause aggregation of coloring materials when contacted.

  According to a second aspect of the present invention, in an ink jet recording method for recording on a recording medium by discharging a plurality of water-based inks from an ink jet recording head, the same ink set is used to form the ink set. In the ink jet recording method, recording is performed by bringing two water-based inks that cause hue of a color material into contact with each other on a recording medium while being in hue.

  According to a third aspect of the present invention, there is provided an ink storage portion storing a plurality of water-based inks, an ink jet recording head for discharging the plurality of water-based inks, and an ink jet recording head from the ink storage portion. An inkjet recording apparatus comprising an ink supply unit for supplying aqueous ink to the inkjet recording apparatus, wherein the plurality of aqueous inks are a plurality of aqueous inks constituting the ink set of the present invention. It is a recording device.

  According to the present invention, a suitable ink set is provided when a color image is formed on plain paper using color inks suitable for the subtractive color mixing method, that is, cyan, magenta, and yellow inks. Specifically, the ink is fixed at high speed, the line marker resistance of the image is good, there is no bleeding between colors, there is no problem in the back-through and scratch resistance, double-sided printing is possible, and the color ink has a single color. There is provided an ink set capable of obtaining a clear image at a high density in both color mixing. In addition, according to the present invention, there is provided an ink jet recording method and an ink jet recording apparatus that can form the above-described excellent image using the ink set.

It is a longitudinal cross-sectional view of the recording head part of an inkjet recording device. It is a cross-sectional view of a recording head portion of the ink jet recording apparatus. FIG. 2 is an external perspective view of a recording head in which the recording head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view of a recording unit. FIG. 3 is a perspective view showing a recording unit in which two recording heads used in the present invention are arranged. It is explanatory drawing which shows an example of the formation method of a recording dot. It is a perspective view showing a recording part in which five recording heads used in the present invention are arranged.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.
The ink set according to the present invention includes a plurality of water-based inks containing a color material, and the surface tension of the plurality of water-based inks is 34 mN / m or less. In the present invention, the surface tension of the water-based ink can be measured by a conventional method. Such surface tension is measured by, for example, a plate method using a platinum plate using an automatic surface tension meter (CBVP-Z type; manufactured by Kyowa Interface Science) in an environment of a temperature of 25 ° C. and a humidity of 50%. it can.

  In addition, the ink set according to the present invention is configured to include a combination of water-based inks (sometimes simply referred to as inks) having hues of cyan, magenta, and yellow as essential inks. Of the three hue ink combinations of cyan, magenta, and yellow, at least two hue ink combinations are composed of two inks that cause the color material to aggregate when they come into contact with each other even though they have the same hue. By satisfying this condition, the effects on the above problems 1) to 5) are remarkably increased, and all of these problems can be solved satisfactorily for the first time. On the other hand, when the ink of only one hue is a set of two inks that cause aggregation of the color material when they come into contact with each other, it is impossible to solve all the above-mentioned problems at the same time. The ink set of the present invention is preferably composed of two inks that cause aggregation of color materials when they come into contact with each other even though all the three hue inks have the same hue.

  In addition, the ink set of the present invention may further have a black hue ink if necessary, and the black hue ink may have the same hue but contact the color material when contacted. It is particularly preferable that it is composed of two ink sets that cause This is more suitable for information printing in which black characters are frequently used.

  Here, the same hue as used in the present invention indicates the following. First, each ink was ejected onto plain paper using an inkjet recording head having an ejection amount of about 4 pl (picoliter), and a formed 1,200 dpi (dot per inch) × 1,200 dpi solid image was visually observed. Observe at. Next, the hue of the image is classified into ten categories (R, YR, Y, GY, G, BG, B, PB, P, RP) of the Munsell symbol based on the Munsell color chart. In the present invention, it can be determined that yellow and YY belong to the same hue for yellow in the hue classification, P and RP belong to the same hue for magenta, and BG, B and PB belong to the same hue for cyan. . Further, in the present invention, the fact that aggregation occurs in two ink sets in which the color materials aggregate when contacted with the same hue is important, and the mechanism of the aggregation reaction is not particularly limited.

Examples of combinations of the first ink and the second ink that form a set in which aggregation occurs include the following modes. Of course, it is not limited to these aspects.
1) A mode in which the polarities of the water-soluble group (hydrophilic group) of the color material in the first ink and the water-soluble group of the color material in the second ink are different. In this embodiment, the water-soluble group may be directly introduced into the colorant molecule by a covalent bond, or may be introduced into a dispersant for dispersing the water-insoluble colorant.
2) A mode in which an ink containing a color material whose solubility is greatly changed by a change in pH is used. For example, a first ink that includes a color material that is insolubilized in an acidic region and is adjusted to be alkaline, and a second ink that includes a color material that is stably dissolved in an acidic region and is adjusted to be acidic. Examples thereof include an ink set adjusted so that the mixed solution becomes acidic.
3) A mode in which a first ink containing a color material that aggregates by reaction with a polyvalent metal and a second ink containing a polyvalent metal salt and a color material that is stable against the polyvalent metal are used. Examples of the color material that aggregates due to the reaction with the polyvalent metal include a color material having a carboxyl group as a water-soluble group.
4) A mode in which a first ink containing a color material that aggregates by reaction with a cationic polymer and a second ink containing a cationic polymer and a color material that is stable to the cationic polymer are used.
5) a first ink containing a color material that aggregates in response to a solvent shock, a solvent that aggregates the color material in the first ink, and a second ink containing a color material that is stable against the solvent shock; A mode of using.

  In addition, the term “aggregation” as used in the present invention refers to the generation of insoluble matter when ink contacts. In most cases, the insoluble matter can be visually determined. For example, the insoluble matter refers to an agglomerate to which it can be confirmed whether or not there is a precipitate when filtered with a filter having a pore diameter of about 1 μm. In the present invention, the color material aggregation reaction caused by the contact of the two inks described above includes the case where the color materials of both the first ink and the second ink are aggregated simultaneously, and either one of the inks. Color materials may be agglomerated.

Hereinafter, the components of the ink used in the present invention will be described in detail.
(Coloring material)
In the present invention, it is the color material in the ink that is the main component of aggregation. In selecting a color material, it is divided into a color material that aggregates itself and a color material that does not aggregate itself but is convenient to use in combination with an aggregating agent that aggregates the color material of the partner ink. These color materials need to be used properly according to the situation. As the color material contained in the ink used in the present invention, either a dye or a pigment can be used as long as it is involved in aggregation. The amount of the coloring material added to the ink is not limited to this range, but is preferably in the range of 0.1% by mass to 15% by mass with respect to the total mass of the ink. More preferably, it is the range of 0.2 mass% or more and 12 mass% or less, More preferably, it is the range of 0.3 mass% or more and 10 mass% or less.

  Further, when the two ink sets are a combination of light and dark inks having different color material densities, and the light ink of the first ink is used as the second ink, it is preferable that the following relationship is satisfied. That is, the absorbance ratio (light ink / dark ink) at the maximum peak wavelength of the second ink (light ink) to the first ink (dark ink) is preferably in the range of 1/10 to 1/2. . In this case, in addition to solving the above-mentioned problems 1) to 5), it is possible to simultaneously solve the problem of graininess of the photographic image when using the ink jet dedicated paper, and to obtain the highest level photographic image. Can do. On the other hand, when it is out of this range, the image density may be too low or too high, and the effect of reducing graininess may not be obtained. In the present invention, the dark ink specifically refers to an ink in which the concentration of the color material contained in the ink is 2.0% by mass or more, and the light ink specifically refers to the ink. This is an ink in which the concentration of the color material contained in the ink is less than 2.0% by mass.

<Dye>
In the present invention, almost all of the water-soluble acid dyes, direct dyes, basic dyes, and reactive dyes described in the color index can be used as the dye used in the ink. Even those not described in the color index can be used as long as they are water-soluble dyes.

  Specific examples of the dye used in the present invention are listed below. For example, those that are stable in the alkaline region and aggregate in the acidic region are acidic dyes and direct dyes. Among them, examples of dyes used for yellow ink include C.I. I. Direct Yellow 173, 142, 144, 86, 132 and C.I. I. Acid yellow 23, 17 and the like. Examples of the dye used in the magenta ink include C.I. I. Acid Red 92, 289, 35, 37, 52 and the like. Examples of the dye used for the cyan ink include C.I. I. Acid Blue 9, 7, 103, 1, 90, C.I. I. Direct blue 86, 87, 199 and the like can be mentioned. Examples of the dye used for the black ink include C.I. I. Food Black 2, C.I. I. Direct black 52, 154, 195 etc. are mentioned.

  On the other hand, those that are stable in the acidic region and aggregate in the alkaline region are basic dyes. Among them, although not particularly limited, examples of suitable dyes used in yellow ink include C.I. I. Basic yellow 21, 28, 40, 51, 67 etc. are mentioned. Examples of the dye used in the magenta ink include C.I. I. Basic red 27, 29, 36, 46, 70, etc. are mentioned. Examples of the dye used for the cyan ink include C.I. I. Basic blue 41, 54, 69, 75, 129 etc. are mentioned. These dyes are appropriately selected depending on the difference in the aggregation mechanism employed.

  Furthermore, as a more suitable thing, the dye from which the solubility with respect to water changes a lot by change of pH is mentioned. Examples of the dye include U.S. Pat. Nos. 5,053,495, 5,203,912, 5,177,195, 5,281,263, 5,374,301, and 5,279,656. 5,296,023 and 5,423,906. These dyes can also be suitably used for utilizing the agglutination reaction. Examples of commercially available dyes include PRO-JET Fast Yellow 2 Liquid, PRO-JET Fast Magenta 2 Liquid, PRO-JET Fast Cyan 2 Liquid, and PRO-JET Fast Black 2 Liquid (trade name, manufactured by Avec). It can be used. Further, examples of the reactive dye described above include C.I. I. Reactive Yellow 95, C.I. I. Reactive Red 226, C.I. I. Reactive Blue 15, C.I. I. Reactive black 5 etc. are mentioned.

<Pigment>
In the present invention, a good effect is also obtained when a pigment is used as the coloring material.
Carbon black is preferably used as the pigment used in the black ink. Examples thereof include carbon black such as furnace black, lamp black, acetylene black and channel black. Among them, the primary particle diameter is 15 nm to 40 nm, the specific surface area by the BET method is 50 m ² / g to 300 m ² / g, the DBP oil absorption is 40 ml / 100 g to 150 ml / 100 g, and the volatile content is 0.5% by mass. What has the characteristic of 10 mass% or less is suitable.

  An organic pigment is suitable as the pigment used in the color ink. Specifically, insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red, water-soluble azo pigments such as ritole red, helio bordeaux, pigment scarlet, permanent red 2B, alizarin, indanthrone, Derivatives from vat dyes such as thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, isoindolinone yellow, Isoindolinone pigments such as isoindolinone orange, benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red Zolone pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo Examples thereof include pigments such as yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinonyl red, and dioxazine violet.

  Further, when the organic pigment is represented by a color index (CI) number, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 55, 74, 83, 86, 93, 97, 98, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 71, C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 202, 209, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Pigment Brown 23, 25, 26 and the like can be exemplified. In the present invention, pigments other than the above can also be used. In particular, among these pigments, C.I. I. Pigment Yellow 13, 17, 55, 74, 93, 97, 98, 110, 128, 139, 147, 150, 151, 154, 155, 180, 185, C.I. I. Pigment Red 122, 202, 209 and C.I. I. More preferably, CI pigment blue 15: 3 and 15: 4 are used. These pigments are dispersed with a dispersant by a usual method.

On the other hand, instead of dispersing the pigment with a dispersant, a self-dispersing pigment in which a water-soluble group is chemically bonded to the surface of the pigment particle directly or via another atomic group is also suitably used in the present invention. it can. Examples of the anionic functional group (water-soluble group) include those obtained by bonding a hydrophilic group as shown below. _{-COO (M2), - SO 3} (M2) 2, -PO 3 H (M2), - PO 3 (M2) 2 ( provided that, M2 in the formulas represents a hydrogen atom, an alkali metal, ammonium or organic ammonium .)

  Among those expressed as “M2” in the hydrophilic group, specific examples of the alkali metal include Li, Na, K, Rb and Cs. Specific examples of organic ammonium include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, monohydroxymethylamine, dihydroxymethylamine, and trihydroxymethylamine.

  Specific examples of the method for producing the pigment include a method of oxidizing carbon black with sodium hypochlorite. According to this method, a carboxyl group and a lactone group, which are hydrophilic groups, can be formed on the surface of carbon black.

By the way, the various hydrophilic groups as described above may be directly bonded to the surface of the pigment, or other atomic groups may be interposed between the pigment surface and the hydrophilic group as described above so as to be hydrophilic. Groups may be indirectly attached to the pigment surface. Here, specific examples of the other atomic groups include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. It is done. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples of combinations of other atomic groups and hydrophilic groups include, for example, —C ₂ H ₄ —COO (M2), —Ph—SO ₃ (M2) ₂ , —Ph—COO (M2) (however, And M2 in the formula is as defined above, and Ph represents a phenyl group).

  When a cationic group is introduced as the water-soluble group, for example, at least one aromatic group such as a phenyl group, benzyl group, phenacyl group or naphthyl group, or a heterocyclic group such as a pyridyl group, and at least It preferably consists of one cationic group. More preferably, the cationic group bonded to the surface of carbon black is a quaternary ammonium group.

  In the present invention, the average particle diameter of the pigment when the pigment is used as the coloring material in the ink is preferably in the range of 50 nm to 200 nm. As a measuring method of the average particle diameter, it can be measured using ELS-8000 (manufactured by Otsuka Electronics Co., Ltd.), Microtrac UPA 150 (manufactured by Nikkiso Co., Ltd.), etc. utilizing laser light scattering.

(Dispersant)
In the present invention, the dispersant used when the pigment is dispersed with the dispersant is not particularly limited as long as it is water-soluble. Specifically, a block copolymer or a random copolymer, a graft copolymer comprising at least two monomers (of which at least one is a hydrophilic monomer) selected from the following monomers: Or these salts etc. are mentioned. Examples of monomers include styrene and its derivatives, vinyl naphthalene and its derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its Derivatives, fumaric acid and derivatives thereof, vinyl acetate, vinyl pyrrolidone, acrylamide, and derivatives thereof. Among these, a block copolymer is a particularly preferable dispersant for carrying out the present invention. By using the block copolymer in the present invention, particularly when the recording head using thermal energy is driven at a high driving frequency, for example, 10 KHz or more, the effect of improving the ink ejection property can be obtained more preferably. It is done. Moreover, it is preferable that the weight average molecular weight of the copolymer used as a dispersing agent is the range of 1,000 or more and 30,000 or less.

  Further, the content of the dispersant in the ink is preferably in the range of 0.5% by mass or more and 10% by mass or less with respect to the total mass of the ink. More preferably, it is the range of 0.8 mass% or more and 8 mass% or less, More preferably, it is the range of 1 mass% or more and 6 mass% or less. On the other hand, when the content of the dispersant is higher than this range, it may be difficult to maintain a desired ink viscosity.

(Aqueous medium)
The ink used in the present invention contains water as an essential component, but the water content in the ink is preferably 30% by mass or more and 95% by mass or less based on the total mass of the ink. Is preferred. In many cases, an aqueous medium in which water and a water-soluble solvent are used in combination is used. Examples of the water-soluble solvent used in combination with water include those conventionally used in ink jet inks. Among these, it is preferable to use ethylene glycol, polyethylene glycol (average molecular weight of 200 or more and 1,000 or less), glycerin, 1,2,6-hexanetriol, ethylene urea, trimethylolpropane, and diglycerin. In the ink used in the present invention, the type and content of the water-soluble solvent used in combination with water are not particularly limited. For example, the content of the water-soluble solvent in the ink is preferably 3% by mass or more and preferably 60% by mass or less with respect to the total mass of the ink.

(Flocculant)
The flocculant contained in the first ink or the second ink constituting the present invention and aggregating the coloring material of the other ink when these two inks are brought into contact is an aggregation mechanism of the coloring material. It is set individually based on this, and is not of a nature to be limited. For example, polyvalent metal salts, acids, alkalis, pH adjusters, cationic polymers and the like are often effective as flocculants.

  First, the polyvalent metal salt will be described. The polyvalent metal salt is effective when aggregating a color material having an anionic functional group, and particularly effective when a color material having a carboxyl group is aggregated. Specifically, for example, magnesium salt, calcium salt, barium salt, iron (II) salt such as inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, organic acid such as acetic acid and hydroxycarboxylic acid, or polyol phosphate ester, etc. , Copper (II) salt, zinc salt, aluminum salt and the like. Among these, preferred are magnesium salt, calcium salt, zinc salt or aluminum salt of nitric acid, sulfuric acid or acetic acid.

  For a color material that is insolubilized and aggregates due to a change in pH, it is effective to introduce a pH adjuster into the other ink so that the color material becomes insoluble when contacted with the ink. Specific examples of the pH adjuster include hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonium hydroxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate and ammonium sulfate, and carbonates. Lithium, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, ammonium carbonate and other carbonates, lithium phosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate , Phosphates such as dipotassium phosphate, tripotassium phosphate, monoammonium phosphate, diammonium phosphate, triammonium phosphate, acetates such as lithium acetate, sodium acetate, potassium acetate and ammonium acetate, hydrochlorides, etc. Is mentioned. These pH adjusters can be used for both the first ink and the second ink, and can be used alone or in combination of two or more.

  Next, a cationic polymer is also effective as a flocculant for a color material having an anionic functional group in the color material. Specifically, for example, polyallylamine hydrochloride, polyamine sulfone hydrochloride, polyvinylamine hydrochloride, chitosan acetate and the like can be mentioned, but of course not limited thereto. Moreover, it is not necessarily limited to the hydrochloride type or the acetate type.

  The content of the above various flocculants in the ink is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more, based on the total mass of the ink. The range is 5% by mass or less.

(Surfactant)
In the ink used in the present invention, it is preferable to contain a surfactant in the ink in order to adjust the surface tension to 34 mN / m or less and to obtain a well-balanced ejection stability. Among these, it is preferable to contain a nonionic surfactant. Of the nonionic surfactants, polyoxyethylene alkyl ethers and ethylene oxide adducts of acetylene glycol are particularly preferable. These nonionic surfactants preferably have an HLB value (hydrophile-lipophile balance) of 10 or more. The content of the surfactant used in this manner is preferably in the range of 0.6% by mass to 5% by mass with respect to the total mass of the ink. More preferably, it is the range of 0.7 mass% or more and 4 mass% or less, More preferably, it is the range of 0.8 mass% or more and 3 mass% or less.

(Other additives)
In addition to the above-described components, the ink used in the present invention includes, as necessary, a viscosity modifier, an antifoaming agent, an antiseptic, and an antifungal agent, in order to obtain an ink having a desired physical property value. Agents, antioxidants, penetrants and the like can be added.

(Inkjet recording method)
Next, an ink jet recording method using the ink set of the present invention will be described.
In the ink jet recording method of the present invention, at least a combination of three-color aqueous inks of cyan, magenta, and yellow is used. Further, for the combination of water inks of at least two hues among the combination of water inks of the three hues, two inks that cause the aggregation of the coloring materials when they are in contact with each other while using the same hue are used. The inkjet recording method of the present invention may be any method as long as the two inks can be separately ejected from the recording head and brought into contact with the recording medium for recording. Ink may be applied on the recording medium first. However, it is more preferable to use a pigment as a coloring material contained in at least one of the inks for the purpose of further improving the fixing property and bleed resistance, and the surface tension is 34 mN / m or less as described above. To do. In addition, the configuration of the ink set for recording includes, for example, at least five inks in the case of recording with inks of three hues of cyan, magenta, and yellow, where the number of ink hues is the smallest.

  Basically, inks of the same hue can fly from individual nozzle rows independently of each other in accordance with an electrical signal, and the same matrix can be recorded. Accordingly, the ink application ratio in recording with two inks having the same hue is not particularly limited, but is preferably in the range of first ink: second ink = 1: 9 to 9: 1. preferable. Further, it is preferable to form an image using it in the range of 2: 8 to 8: 2. If it is out of the above range, the color material aggregation effect of the two inks described above becomes insufficient, and the desired effect may not be obtained.

  In addition, as a method of allowing the first ink and the second ink to coexist on the recording medium, both inks may be attached to the same location of the recording dots on the recording medium, or alternatively, adjacent dots may be alternately displayed. Both inks may be applied. However, both inks need to contact on the recording medium. In addition, when the first ink is applied prior to the second ink, the time from when the first ink is applied to the recording medium to when the second ink is attached is not particularly limited. In order to carry out the invention more effectively, it is preferably within several seconds, particularly within 3 seconds.

(Inkjet recording device)
Next, the ink jet recording apparatus used in the present invention will be described. As an ink jet recording apparatus suitable for performing recording using the ink set of the present invention, an ink jet recording apparatus that applies thermal energy corresponding to a recording signal to ink in a recording head chamber and generates ink droplets by the thermal energy. Is mentioned.

  A configuration example of a recording head which is a main part of the ink jet recording apparatus is shown in FIGS. The recording head 13 is a glass, ceramic or plastic plate having a groove 14 through which ink passes, and a heating head 15 having a heating resistor used for thermal recording (the head is shown in the figure, but is not limited thereto). Is not obtained). The heat generating head 15 includes a protective film 16 formed of silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heat generating resistor layer 18 formed of nichrome or the like, a heat storage layer 19, and a substrate with good heat dissipation such as alumina. 20. The ink 21 has a discharge orifice (fine hole) 22 and forms a meniscus 23 by a pressure (not shown). Now, when an electrical signal is applied to the electrodes 17-1 and 17-2, the region indicated by n of the heat generating head 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact therewith. Then, the meniscus 23 protrudes by the pressure, and the ink 21 is ejected to form a recording droplet 24 from the ejection orifice 22 and fly toward the recording medium 25.

  FIG. 3 shows an external view of a multi-nozzle head in which a large number of nozzles shown in FIG. 1 are arranged. The multi-nozzle head is manufactured by adhering a glass plate 27 having multi-grooves 26 and a heat-generating head 28 similar to that described in FIG. 1 is a cross-sectional view of the recording head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along line AB in FIG. When incorporated in a recording unit, the multi-nozzle head has a multilayer structure, and in the case of the present invention, at least five multi-nozzle rows are required.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating the head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member. One end of the blade 61 is held by a blade holding member to become a fixed end, and forms a cantilever. The blade 61 is disposed at a position adjacent to a recording area by the recording head.

  In the case of this example, the recording head is held in a protruding form in the moving path. Reference numeral 62 denotes a cap on the ejection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ejection port surface, and performs capping. It has a configuration. Further, reference numeral 63 denotes an ink absorber disposed adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head. The blade 61, the cap 62, and the ink absorber 63 constitute a discharge recovery portion 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ink discharge port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface on which the discharge ports are arranged. Reference numeral 66 denotes a recording head mounted with the recording head 65. It is a carriage for performing 65 movements. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area by the recording head 65 and its adjacent area can be moved.

  Reference numeral 51 denotes a paper feed unit for inserting a recording medium, and 52 denotes a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the discharge port surface of the recording head 65, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses.

  In the above configuration, when the recording head 65 returns to the home position due to the end of recording or the like, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. . As a result, the ejection port surface of the recording head 65 is wiped. When the cap 62 is in contact with the ejection port surface of the recording head 65 for capping, the cap 62 moves so as to protrude into the moving path of the recording head.

  When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as the above-described wiping position. As a result, even in this movement, the ejection port surface of the recording head 65 is wiped.

  The above-mentioned movement of the recording head 65 to the home position is not only at the end of recording or at the time of ejection recovery, but also at the home position adjacent to the recording area at a predetermined interval while the recording head 65 moves the recording area for recording. The wiping is performed along with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge 45 that stores ink supplied to the recording head via an ink supply unit, for example, a tube. Here, reference numeral 40 denotes an ink containing portion for containing supply ink, for example, an ink bag, and a rubber stopper 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the recording head. An ink absorber 44 receives waste ink. As the ink containing portion, it is preferable for the present invention that the liquid contact surface with the ink is formed of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to one in which the recording head and the ink cartridge as described above are separated, and is preferably used in an apparatus in which they are integrated as shown in FIG. . In FIG. 6, reference numeral 70 denotes a recording unit, which includes an ink storage portion (a part of or all of the ink absorber is stored) that stores a plurality of inks. The ink storage unit may be configured such that each color ink can be replaced independently. The ink storage unit is configured to eject ink droplets individually from the recording head unit 71 having a plurality of multi-nozzle rows. In the case of the present invention, at least five ink columns are required, and when there are not enough ejected ink columns in the unit shown in the figure, a plurality of printing units shown in the figure are used as a recording unit. You can also As the material of the ink absorber, it is preferable for the present invention to use polyurethane, cellulose, polyvinyl acetate, or polyolefin resin.

  Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the recording unit with the atmosphere. The recording unit 70 is used in place of the recording head shown in FIG. 4 and is detachable from the carriage 66.

  As an example of the ink jet recording apparatus used in the present invention, an ink jet recording apparatus that discharges ink droplets by applying thermal energy to ink has been described above. However, the present invention can also be used in other inkjet recording apparatuses such as a piezo method using a piezoelectric element.

  When carrying out the ink jet recording method of the present invention, for example, a recording apparatus equipped with a headset in which two recording heads of FIG. 3 are arranged on a carriage 66 can be used. FIG. 7 shows an example of the headset. Reference numerals 81 and 82 denote recording heads that are individually mounted with inks that cause aggregation of color materials when mixed while having the same hue. These recording heads are arranged in the above-described recording apparatus, and ink is ejected in accordance with a recording signal.

  Further, in a recording unit of another embodiment, for example, a recording apparatus in which five recording heads of FIG. FIG. 9 is an example of the simplest configuration of the present invention. 81 is a yellow ink, 82 is a magenta first ink, 83 is a magenta second ink, 84 is a cyan first ink, and 85 is a cyan second ink. It is a recording head. The first ink and the second ink of each hue described above are aggregated by mixing. These recording heads are arranged in the above-described recording apparatus, and ink is ejected according to a recording signal.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “parts” and “%” are based on mass unless otherwise specified. First, a method for producing pigments and further pigment dispersions contained in the inks constituting the ink sets of Examples and Comparative Examples will be described.

(Manufacture of pigments and pigment dispersions)
<Production of self-dispersing cationic pigment 1>
In a solution of 3.08 g of H ₃ N ⁺ C ₆ H ₄ N ⁺ (CH ₃ ) ₃ Cl ^−. I ⁻ dissolved in 30 g of water, 1.69 g of silver nitrate was added with stirring. The generated precipitate was removed by filtration, and the obtained filtrate was stirred in a suspension in which 10 g of carbon black having a specific surface area of 230 m ² / g and DBPA of 70 m1 / 100 g was dispersed in 70 g of water. Added while. Next, 2.25 g of concentrated hydrochloric acid was added, and then a solution of 0.83 g of sodium nitrite dissolved in 10 g of water was added to obtain a diazonium having an NN ⁺ C ₆ H ₄ N ⁺ (CH ₃ ) ₃ group. The salt reacted with carbon black to generate nitrogen gas. After the nitrogen gas bubbles stopped, the dispersion was dried in an oven at 120 ° C. As a result, a self-dispersing cationic pigment 1 having a C ₆ H ₄ N ⁺ (CH ₃ ) ₃ group on the surface of carbon black was obtained. DBPA (Di-Butyl phthalate Adsorption) is a value obtained by measuring the amount of oil absorption using dibutyl phthalate.

<Production of self-dispersing anionic pigment dispersion 1>
To a solution of 5 g of concentrated hydrochloric acid dissolved in 5.3 g of water, 1.58 g of anthranilic acid was added at 5 ° C. This solution was always kept at 10 ° C. or lower by stirring with an ice bath, and a solution obtained by adding 1.78 g of sodium nitrite to 8.7 g of water at 5 ° C. was added. Further, after stirring for 15 minutes, 20 g of carbon black having a specific surface area of 320 m ² / g and DBPA of 120 m1 / 100 g was added in a mixed state. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was Toyo Filter Paper No. 2 (manufactured by Advantech Co., Ltd.), the pigment particles were sufficiently washed with water, dried at 110 ° C. open, and water was added to the pigment to prepare a pigment aqueous solution having a pigment concentration of 10%. By the above method, a self-dispersing anion pigment dispersion 1 having a hydrophilic group (carboxyl group) bonded to the surface via a phenyl group was obtained.

<Production of Resin Dispersion Type Anion Pigment Dispersion 1>
First, an ABC type block polymer having an acid value of 350 mgKOH / g and a weight average molecular weight of 7,500 was synthesized by anionic living polymerization using benzyl methacrylate, methacrylic acid and ethoxyethylene glycol methacrylate as raw materials. Further, the solution was neutralized with an aqueous potassium hydroxide solution and diluted with ion exchange water to prepare a homogeneous 50% aqueous polymer solution. 100 g of the above polymer solution, C.I. I. 100 g of Pigment Red 122 and 300 g of ion exchange water were mixed and mechanically stirred for 0.5 hour. The mixture was then processed using a microfluidizer by passing the mixture through the interaction chamber five times under a liquid pressure of about 10,000 psi (about 70 MPa). Further, the dispersion obtained above was centrifuged (12,000 rpm, 20 minutes) to remove the non-dispersion containing coarse particles, thereby obtaining a magenta resin-dispersed anion pigment dispersion 1. The obtained resin dispersion type anion pigment dispersion 1 had a pigment concentration of 10% and a dispersant concentration of 6%.

<Production of Resin Dispersion Type Anion Pigment Dispersion 2>
In the production of the resin-dispersed anion pigment dispersion 1, C.I. I. In place of Pigment Red 122, C.I. I. A cyan resin-dispersed anion pigment dispersion 2 was obtained in the same manner except that CI Pigment Blue 15: 3 was used. The obtained resin dispersion type anion pigment dispersion 2 had a pigment concentration of 10% and a dispersant concentration of 5.5%.

(Preparation of ink)
Next, preparation examples of inks used in Examples and Comparative Examples of the present invention will be described. The following inks were prepared by mixing all the components constituting the ink (100 parts in total) and then stirring for 1 hour. A filter having a pore size of 0.45 μm for dye ink and a pore size of 2.5 μm for pigment ink Was performed on the basis of filtration. In addition, ion-exchange water was used for water. The surface tension of each ink is 34 mN / m or less.

<Preparation of yellow ink 1>
An ink was prepared using the following ingredients. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Direct yellow 86 2 parts · Glycerin 10 parts · Diethylene glycol 10 parts · Isopropanol 2 parts · Acetylene glycol ethylene oxide adduct (Product name: Acetyleneol EH, manufactured by Kawaken Fine Chemicals,
HLB "13"). Hereinafter referred to as acetylenol EH. ) 1 part, water remaining

<Preparation of yellow ink 2>
An ink having the following constitution was prepared using the following dye manufactured by Avecia (PRO-JET Fast series) whose water solubility rapidly decreases in the acidic region. The pH was adjusted to 9.0 with lithium hydroxide after mixing all the following components.
・ Yellow 2 Liquid (trade name) 50 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Ammonium sulfate 0.5 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of yellow ink 3>
An ink was prepared using the following ingredients. The pH was adjusted to pH 8 with sodium hydroxide and further adjusted to pH 4.0 with citric acid after mixing all the following components.
・ C. I. Reactive Yellow 95 2 parts ・ Diethylene glycol 20 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of magenta ink 1>
Using the resin dispersion type anion pigment dispersion 1 obtained above, an ink having a pigment concentration of 2.5% and a dispersant concentration of 1.5% was prepared from the following components. The pH was adjusted to 8.5 with potassium hydroxide after mixing all the following components.
・ Resin dispersion type anion pigment dispersion 1 25 parts ・ Glycerin 10 parts ・ Ethylene urea 2 parts ・ 2-Pyrrolidone 3 parts ・ 1,2,6-hexanetriol 5 parts ・ Polyoxyethylene cetyl ether (ethylene oxide addition number 20, HLB17) 0.1 part acetylenol EH 1 part water balance

<Preparation of magenta ink 2>
An ink was prepared using the following ingredients. The pH was adjusted to 4.5 with acetic acid.
・ C. I. Basic Red 36 2.5 parts · Glycerin 10 parts · Diethylene glycol 10 parts · Isopropanol 2 parts · Polyallylamine (average molecular weight 1,300) 2 parts · Benzalkonium chloride 0.3 parts · Acetylenol EH 1 part · Water balance

<Preparation of magenta ink 3>
An ink was prepared using the following ingredients. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Acid Red 52 3 parts, Glycerol 10 parts, Diethylene glycol 10 parts, Isopropanol 2 parts, Acetylenol EH 1 part, Water balance

<Preparation of magenta ink 4>
An ink having the following constitution was prepared using the following dye manufactured by Avecia (PRO-JET Fast series) whose water solubility rapidly decreases in the acidic region. The pH was adjusted to 9.0 with lithium hydroxide after mixing all the following components.
・ Magenta 2 Liquid (trade name) 50 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of magenta ink 5>
A magenta light ink was prepared using the following components. The pH was adjusted to pH 4.0 by adding sodium hydride after mixing all the following constituents and further adding citric acid.
・ C. I. Reactive Red 226 0.5 parts ・ Diethylene glycol 20 parts ・ Isopropanol 2 parts ・ Ammonium sulfate 0.5 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of magenta ink 6>
A magenta light ink was prepared using the following components. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Acid Red 52 0.5 part ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of cyan ink 1>
Using the resin dispersion type anion pigment dispersion 2 obtained above, an ink having a pigment concentration of 2.5% and a dispersant concentration of 1.375% was prepared from the following components. The pH was adjusted to 8.5 with potassium hydroxide after mixing all the following components.
・ Resin dispersion type anion pigment dispersion 2 25 parts ・ Glycerin 10 parts ・ Ethylene urea 2 parts ・ 2-Pyrrolidone 3 parts ・ 1,2,6-hexanetriol 5 parts ・ Polyoxyethylene cetyl ether (ethylene oxide addition number 20, HLB17) 0.1 part acetylenol EH 1 part water balance

<Preparation of cyan ink 2>
An ink was prepared using the following ingredients. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Direct Blue 86 3 parts ・ Glycerin 5 parts ・ Diethylene glycol 10 parts ・ 1,2,6 hexanetriol 5 parts ・ Isopropanol 2 parts ・ Magnesium nitrate 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of cyan ink 3>
An ink was prepared using the following ingredients. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Direct Blue 86 3 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of cyan ink 4>
An ink having the following constitution was prepared using the following dye manufactured by Avecia (PRO-JET Fast series) whose water solubility rapidly decreases in the acidic region. The pH was adjusted to 9.0 with lithium hydroxide after mixing all the following components.
・ Cyan 2 Liquid (trade name) 40 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Ammonium sulfate 0.5 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of cyan ink 5>
A cyan light ink was prepared using the following ingredients. The pH was adjusted to pH 4.0 by adding sodium hydride after mixing all the following constituents and further adding citric acid.
・ C. I. Reactive Blue 15 0.5 part ・ Diethylene glycol 20 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of cyan ink 6>
A cyan light ink was prepared using the following components. The pH was adjusted to 8.5 with sodium hydroxide.
・ C. I. Direct Blue 86 0.5 part ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of black ink 1>
Using the self-dispersing anionic pigment dispersion 1 obtained above, an ink having the following constitution was prepared. The pH was adjusted to pH 8.5 with lithium hydroxide after mixing all the following components.
・ Self-dispersing anionic pigment dispersion 1 30 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of black ink 2>
Using the self-dispersing cationic pigment 1 obtained above, an ink having the following constitution was prepared. The pH was adjusted to pH 5 with acetic acid after mixing all the following components.
・ Self-dispersing cationic pigment 1 3 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of black ink 3>
An ink having the following constitution was prepared using the following dye manufactured by Avecia (PRO-JET Fast series) whose water solubility rapidly decreases in the acidic region. The pH was adjusted to 9.0 with lithium hydroxide after mixing all the following components.
・ Black 2 Liquid (trade name) 60 parts ・ Glycerin 10 parts ・ Diethylene glycol 10 parts ・ Isopropanol 2 parts ・ Ammonium sulfate 0.5 parts ・ Acetylenol EH 1 part ・ Water balance

<Preparation of black ink 4>
An ink was prepared using the following ingredients. The pH was adjusted to pH 4.0 by adding sodium hydride after mixing all the following constituents and further adding citric acid.
・ C. I. Reactive Black 5 3 parts ・ Diethylene glycol 20 parts ・ Isopropanol 2 parts ・ Acetylenol EH 1 part ・ Water balance

  As described above, the prepared inks were mixed between the inks of the same hue, and the presence or absence of occurrence of aggregation of the coloring material was confirmed. The obtained results are shown in Tables 1 to 4.

(Creation of ink sets of Examples 1 to 4 and Comparative Examples 1 to 3)
The ink sets of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared with the combinations shown in Table 5 using each ink of each hue prepared above.

(Evaluation)
Next, recording was performed on commercially available copy paper (PB paper made by Canon Inc., 4024 paper made by Xerox Corp.) and bond paper (ploverBond) using the ink sets of Examples and Comparative Examples obtained above. The ink jet recording apparatus used is BJ-W9000 (trade name: manufactured by Canon Inc., an ink jet printer) equipped with two recording heads each having six print rows of 256 nozzles per color. Each of the recording heads uses 3 to 4 nozzle rows, and the first recording head is loaded with the first ink, and the second recording head is loaded with the second ink. It was. The drive frequency of BJ-W9000 (trade name: manufactured by Canon Inc., inkjet printer) was 5 kHz. As a method of forming a recording image, two recording heads are used, and 50% duty is recorded with one recording head so that ink of the same hue is solid and the total becomes 100% duty (duty). The remaining 50% duty was recorded with the other recording head. The recording dot forming method was a recording in which the first ink and the second ink were alternately applied to adjacent dots, as shown in FIG.

  The printed matter obtained using the ink sets of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated for the back-through property, the line marker resistance, and the bleed resistance, and the evaluation results are shown in Table 7. The recorded material was evaluated by the following method.

<Betrayal>
The penetration property of the solid print portion of each hue ink was evaluated according to the following evaluation criteria.
◯: No print-through is observed in any printed part.
Δ: Slightly see-through is observed in some printed parts.
X: Clear show-through is recognized in a plurality of printed portions.

<Line marker resistance>
The printed part of each hue ink was marked once 30 seconds after printing with a normal fluorescent pressure using a yellow fluorescent pen and a spot writer (trade name) manufactured by Pilot. And the marked part was observed visually and the line marker resistance was evaluated according to the following evaluation criteria.
◯: No blur or white background stain is observed on the printed matter, and the pen tip is not dirty.
Δ: The printed material has no white background stains, but the pen tip is slightly dirty.
X: Dirt on the white background is recognized on the printed matter.

<Bleed resistance>
Immediately after printing, the solid portions of other hues are further printed adjacent to all the solid portions of each hue ink, and the appearance of the boundary portion is visually observed. The bleeding property was evaluated.
○: Bleeding at all boundaries is within an allowable range.
Δ: Slight bleeding is observed at the boundary depending on the combination of hues.
X: Bleeding is recognized by a combination of a plurality of hues.

<Example 5 and Comparative Example 4>
Example 5 and Comparative Example 4 are examples in which light ink is used as the second ink of cyan and magenta. Table 6 shows the configurations of these ink sets. In the cyan inks of Example 5 and Comparative Example 4, the absorbance ratio at the maximum peak wavelength of the second ink (light ink) to the first ink (dark ink) was 0.2. In the magenta ink of Example 5 and Comparative Example 4, the absorbance ratio at the maximum peak wavelength of the second ink (light ink) to the first ink (dark ink) was 0.2. Further, the recording apparatus and the recording method used in the evaluation of Example 5 and Comparative Example 4 were in accordance with the conditions in Example 1. However, when forming a solid part of ink having the same hue only in the recording density, The duty of the first ink and the second ink was set to 130% in total. Note that the first ink was recorded at 100% duty with one recording head, and the second ink was recorded with 30% duty with the other recording head. The obtained evaluation results are shown in Table 7.

  In addition, about the said recorded matter obtained using the ink set of Examples 1-5, when color development was confirmed visually, in all the printing parts of each hue ink, color development was favorable and a clear image was formed. It has been confirmed. That is, since the recorded matter obtained using the ink sets of Examples 1 to 5, the ink is fixed at high speed, the color development is excellent, the bleeding is difficult, the line marker resistance, and the back-through property are also good. It can be said that it has excellent duplex printing aptitude.

Claims (7)

  An ink set comprising a plurality of water-based inks containing a color material discharged from an inkjet recording head, wherein the surface tension of the plurality of water-based inks is 34 mN / m or less, and the ink set is at least , Cyan, magenta, and yellow, and a combination of aqueous inks of at least two of the three hues that are in the same hue but cause aggregation of coloring materials when in contact with each other. An ink set comprising an aqueous ink.   2. The ink set according to claim 1, wherein each of the combinations of the three-color water-based inks is composed of two water-based inks that cause aggregation of coloring materials when they come into contact with each other even though they have the same hue.   3. The ink according to claim 1, further comprising a black hue ink, wherein the black hue ink is composed of two water-based inks that cause aggregation of the coloring material when in contact with each other while being in the same hue. set.   The ink according to any one of claims 1 to 3, wherein the color material contained in at least one of the two water-based inks that causes aggregation of the color material when in contact with each other while having the same hue is a pigment. set.   At least one of the combinations of the water-based inks of at least two hues is a combination of dark and light inks having different color material densities, and the absorbance ratio of the light ink to the dark ink at the maximum peak wavelength is in the range of 1/10 to 1/2. The ink set according to any one of claims 1 to 4.   In an ink jet recording method for recording on a recording medium by discharging a plurality of water-based inks from an ink jet recording head, the ink set according to any one of claims 1 to 5 is used to form the same ink set. An ink jet recording method, wherein recording is performed by bringing two water-based inks that cause color material aggregation when in contact with each other on a recording medium while being in hue.   Ink storage unit storing each of a plurality of water-based inks, an ink jet recording head for discharging the plurality of water-based inks, and an ink supply unit for supplying water-based ink from the ink storage unit to the ink-jet recording head An inkjet recording apparatus comprising: the plurality of water-based inks being a plurality of water-based inks constituting the ink set according to any one of claims 1 to 5. .

Images